Composite materials containing both a fibrous reinforcement material and a resin matrix or resin, have become of increasing importance. Such materials combine an excellent strength with a very low weight, which makes them the first choice for weight-sensitive applications, in particular in the aircraft and energy industries.
There are numerous methods for the fabrication of composite structures, including but not limited to thermoforming polymeric matrices and autoclave processing. However, all are either labor intensive, more costly than using purely metallic materials, not applicable to moderate to high volume applications, or do not result in structurally efficient structures having a desired strength to weight ratio.
NL8104019 discloses a process for producing wind turbine blades from composite material comprising extruded cured fibre reinforced elements in combination with conventional composite materials comprising a resin matrix in combination with a fibrous reinforcement material.
Conventional pultrusion processing methods have moderate production rates for heat-cured, pultruded, composite structures. However, generally, a limitation of pultrusion processes is that a pultrusion process is adapted only to produce elongated parts of uniform cross-section. This is due in part to the nature of the process itself. Because the process operates by pulling long continuous reinforcing fibres through the various unit operations, it naturally forms elongated composites in which the reinforcing fibres are aligned in the direction of the pultrusion.
In the production of pultruded composite structures thermoplastic and thermoset resin matrices are widely used. For structural applications, thermoset resin such as epoxy, vinylester, polyester and polyurethane resins are better suited as they provide structurally efficient composite structures which have a better mechanical performance to weight ratio than comparable structures manufactured from thermoplastic resins. Once cured, thermoset resins cannot be subsequently thermoformed or shaped in any other manner, yet it is necessary to cure the thermoset resin in the die in order to bind the fibres together and to create the desired cross-sectional shape.
Usually, in these processing methods a resin system is employed that sacrifices structural performance for rapid processing. Therefore, conventional pultruded structures are generally unsuitable for primary structural applications due to their less than optimal structural performance. Lower structural performance is due to non-optimal fibre orientations in the fabric and the necessity of using rapid curing resins that have non-optimal structural performance. Incomplete impregnation of resin in the fibre and also moisture which leads to voids in laminates are common problems in conventional pultrusion methods. Wear and tear of the pultrusion apparatus is also an issue with conventional pultrusion systems, particularly wear and tear caused by the contact of abrasive fibre materials with the walls of the apparatus. Very high pullforces may also be required to pull the fibre through the pultrusion apparatus, and difficulties in maintaining a constant rate of fibre flow through the apparatus with such high pullforces may lead to inconsistencies in resin impregnation into the fibre and/or reductions in surface quality.
The invention aims to obviate or at least mitigate the above described problems and/or to provide improvements generally.